Square users can now opt in to an automatic payment system that doesn't even require them to take a phone out.

Any Square user can set up an "automatic tab" at a store or with a merchant they like with Square's updated Card Case app. The merchant can then verify your name with your face and charge you for a transaction when you're in the store.

You receive a notification through the Square application when your tab is open and after you've been charged. But when we asked what kind of protection Square users had from unauthorized transactions, a Square spokesperson stressed that the service is opt-in.

"Card Case’s geo-fencing features are 100% opt-in," Square spokesperson Katie Baynes told Business Insider. "It will only open auto tabs for merchants that you have explicitly told it to. If you turn on auto-open for one merchant, it won’t be on for the merchant next door."

That means merchants can charge you if you are just walking in range of the store without buying anything, as long as you're within 100 meters of the store. The transactions are still linked to your credit card, so you are assuming the same risk for an unauthorized transaction that you are assuming when you sign up for a credit card, Baynes said.

The odds of that happening are probably pretty low if you are only opting in to automatic tabs with merchants you trust. But it's an interesting bet — Square is giving up a layer of security for the sake of convenience.

Square is known for its credit card reader, which plugs into a headphone jack on a smartphone and feeds credit card information into the app.